From the Guidelines
A urine protein/creatinine ratio above 200 mg/g is considered a red flag in patients with renal insufficiency. This is based on the position statement of the National Kidney Foundation (NKF) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) 1. The following ratios are considered abnormal:
- Less than 200 mg/g: normal range
- 500 to 1,000 mg/g: very high levels of proteinuria, where measurement of total protein instead of albumin on a spot urine sample is acceptable Key points to consider when interpreting urine protein/creatinine ratio include:
- The ratio is a convenient spot test that correlates well with 24-hour urine protein measurements
- Persistent elevation requires further investigation, including possible nephrology referral, especially when accompanied by declining glomerular filtration rate (GFR)
- Regular monitoring of urine protein/creatinine ratio in patients with renal insufficiency is essential for tracking disease progression and evaluating treatment effectiveness, as indicated by the NKF and NIDDK position statement 1.
From the Research
Urine Protein/Creatine Ratio in Renal Insufficiency
The urine protein/creatinine ratio is a useful marker for assessing proteinuria in patients with kidney diseases. According to a study published in 2010 2, the morning urinary protein-to-creatinine ratio is a reliable estimator of 24-hour proteinuria in patients with kidney diseases.
Red Flag Numbers
The study found that a protein-to-creatinine ratio of:
- 0.25 g/g is a reliable predictor of 24-hour urine total protein equivalent "thresholds" at 0.2 g/day (sensitivity 0.90; specificity 0.96)
- 0.66 g/g is a reliable predictor of 24-hour urine total protein equivalent "thresholds" at 1.0 g/day (sensitivity 1.00; specificity 0.91)
- 2.55 g/g is a reliable predictor of 24-hour urine total protein equivalent "thresholds" at 3.5 g/day (sensitivity 1.0; specificity 0.97)
Another study published in 2010 3 found that a total protein:creatinine ratio (TPCR) threshold of 100 mg/mmol had a higher sensitivity (94% vs 79%) but lower specificity (88% vs 95%) than an albumin:creatinine ratio (ACR) of 70 mg/mmol to predict 1 g/day of total proteinuria.
Key Points
- The urine protein/creatinine ratio is a useful marker for assessing proteinuria in patients with kidney diseases.
- A protein-to-creatinine ratio of 0.25 g/g, 0.66 g/g, and 2.55 g/g can be used as reliable predictors of 24-hour urine total protein equivalent "thresholds" at 0.2 g/day, 1.0 g/day, and 3.5 g/day, respectively.
- A TPCR threshold of 100 mg/mmol can be used to predict 1 g/day of total proteinuria with high sensitivity but lower specificity compared to ACR.
- The diagnostic performance of both TPCR and ACR varies substantially with age and gender, and should be taken into consideration when interpreting results 3.